Urine is one of the most useful health condition indices within the human body. Changes in the urine color, odor, and consistency can provide important clues about the person's health status. Urine reflects all of the inner workings of the body and contains a wide variety of compounds and metabolic by-products.
Urine is an important part of the body's disposal process. Its job is to remove the extra water and water-soluble waste the kidneys have filtered from the blood. The urine is there primarily to remove toxins that would otherwise build up in the body. Additionally, urine can reveal what the person has been eating and how much they have been drinking As such, the analysis of urine has, for hundreds of years, been one of the ways physicians have assessed various health conditions. As an example, increased concentration of ammonia in urine reflects dehydration. The concentration of ammonia is directly proportional to the extent of dehydration. While ammonia volume is related to fluid intake, it is the concentration of ammonia that reflects the (de)hydration status.
A regular urine test may be done to check the different components of urine. The test can give information about person's health and problems they may have. However urine tests suffer from different issues, including awkward handling of urine, and costly and time-consuming detection of the substance of interest. Therefore, urine tests are only performed sporadically and not automatically during every toilet visit. They are therefore not suitable for tracking day-to-day changes in a person's health status (e.g. for tracking dehydration in elderly).
Recent advances in gas sensing technology, signal processing, and diagnostic algorithms have created chemical sensing and identification devices called “electronic noses” or “e-noses”. These sensor devices are capable of detecting, identifying, and discriminating many types and sources of a wide diversity of chemical species and mixtures of compounds, present in sampled air derived from any source. Therefore, electronic noses are ideal instruments for biomedical uses because of their versatility, low cost, rapid output of results, and capability of continuous operation for physiological monitoring purposes.
A problem with e-nose technology is that, without knowledge of the environment (temperature, volume, flow, distance to source) in which the e-nose is used, concentration of target gases cannot be determined. Furthermore, the output of an e-nose is also affected by small variations in common air constituents such as water or carbon dioxide and variations in temperature.
US 2010/0061889 discloses an apparatus and method for providing results of urine and/or gas analysis. It describes a system with a sensor either in contact with urine or detecting feces gas. The problem of calibration with respect to the nature of the environment in which the sensor is used is not addressed.